Preparation of thiophosphoryl halides

ABSTRACT

ALKYLPHOSPHONOTHIOIC DICHLORIDE-ALUMINUM TRIHALIDE COMPLEXES, WHICH CAN BE PRODUCED BY REACTING THIOPHOSPHORYL HALIDE WITH AN ALKYL ALUMINUM SESQUIHALIDE OR TRIALKYL ALUMINUM, CATALYZE THE FORMATION OF THIOPHOSPHORYL HALIDE FROM SULFUR AND PHOSPHORUS TRIHALIDE.

United States Patent Ofice 3,582,293 Patented June 1, 1971 Int. Cl. C01b 25/10 US. Cl. 23-368 16 Claims ABSTRACT OF THE DISCLOSURE Alkylphosphonothioic dichloride-aluminum tn'halide complexes, which can be produced by reacting thiophosphoryl halide with an alkyl aluminum sesquihalide or trialkyl aluminum, catalyze the formation of thiophosphoryl halide from sulfur and phosphorus trihalide.

BACKGROUND OF THE INVENTION It is known in the art that a thiophosphoryl halide can be produced by reacting phosphorus trichloride and sulfur according to the following equation:

Prior workers have also discovered that this process can be catalyzed by various substances. In this regard, reference is made to US. Pats. Nos. 2,715,561, 2,802,717, 2,850,353, 2,850,354, 2,911,281, and 2,915,361. The Cook patent, US. 2,591,782, teaches that aluminum trihalides are suitable catalysts.

German Pat. No. 1,235,911 teaches that alkylphosphonothioic dichlorides can be prepared in low yield by reacting thiophosphoryl trihalides with trialkyl aluminums. Alkylphosphonothioic dichlorides are useful as chemical intermediates. One method for their use is disclosed in US. 3,024,278.

The U8. patent mentioned last above and the German patent, supra, demonstrate that thiophosphoryl halides are useful materials. A need exists for an economical preparation of these compounds, and this invention satisfies that need. More particularly, this invention satisfies two main objects:

the economical utilization of aluminum values in the synthesis of thiophosphoryl halides, and

provision of a catalytic system especially suited to a reaction sequence for the preparation of alkylthiophosphoryl dihalides through a thiophosphoryl halide intermediate.

SUMMARY OF THE INVENTION The essence of this invention is the discovery that complexes of aluminum halides and alkylphosphonothioic dihalides catalyze the formation of thiophosphoryl trihalides from sulfur and phosphorus trihalides. The catalytic complex need not be pure. Rather, it is advantageous to use the complex in the reaction mixture produced by reacting a thiophosphoryl trihalide with an alkyl aluminum sesquihalide or trialkyl aluminum.

DESCRIPTION OF PREFERRED EMBODIMENTS A preferred embodiment comprises a process for the preparation of a thiophosphoryl halide, said process comprising reacting sulfur and a phosphorus trihalide at a temperature of from about 20 to about 120 C., said process being catalyzed by a catalytic quantity of a cata- -lytic complex having the formula RPSX -AlX wherein R is an alkyl group having up to six carbon atoms, and X is a halogen of atomic number 17 to 35.

Although all the catalysts having the formula as defined above can be used in the process of this invention, certain compounds are preferred. Compounds wherein all halogens are the same comprise the first class of preferred catalysts. Second, chlorides are more highly preferred. Of these the methyl and ethyl compounds are most preferred. In other words, the most preferred catalysts are CH PSCl -AlCl and C H PSCl -AlCl As illustrated by the examples below, the catalysts of this invention are preparable by two processes illustrated by the following equations:

The processes of Equations 2 and 3 are both conducted by simply mixing the reactants. To achieve desirable yields in reasonable reaction times, both processes are carried out at temperatures within the range of from about 50 C. to about 130 C. The trialkyl aluminums are preferably reacted at temperatures from about 65 to about C. On the other hand, the sesquihalides are preferably reacted at temperatures from about 70 to about C.

Reaction pressure is not critical; the reaction proceeds well at ambient pressure. Greater or lesser pressures (for example, 0.25 to 3000 atm.) can be used, if desired. Usually reaction times of up to 18 hours are sufficient. In many instances, the reactions are complete in less than eight hours, e.g. one to six hours. Usually best results are achieved when 1.0 to about 1.2 theories of aluminum compound are employed per each mole of PSX One theory is the amount of aluminum alkyl or aluminum sesquihalide (on a molar basis) required to react with one mole of thiophosphoryl halide to form a monoalkylated product according to Equations 2 or 3.

To achieve highest yields of the catalytic complexes, the reaction is carried out by reacting the thiophosphoryl halide and the aluminum sesquihalide (or aluminum alkyl) without adding any common hydrocarbon solvent to the reaction zone. Any minor amount of hydrocarbon solvent present as an impurity in the starting materials is not overly deleterious. In other Words, it is not necessary to carefully purify the starting materials to remove any traces of hydrocarbon solvent. Thus, it is possible to use readily available forms of the reactants.

The exact nature of these catalytic complexes is not known. Presumably, the aluminum trihalide moiety is coordinated-through the aluminum atom-to the sulfur atom in the phosphonothioic dichloride moiety. Complexes between aluminum chloride and alkylphosphonothioic dichlorideswherein the alkyl radical has up to six carbon atomshave limited solubility in refined mineral oil. In fact, the complex CH PSCl -AlCl is appreciably insoluble therein. It is a liquid at ambient temperature.

The complexes can be broken by pouring over ice. Alternatively, they can be disrupted by treatment with dioxane or an alkali metal halide such as sodium chloride. Such treatment is illustrated by the following equation:

(4) RPSX AlX +NaX- RPSX +NaAlX When the process of this invention is used in a reaction sequence directed ultimately to the preparation of alkylphosphonothioic dichlorides, it is advantageous to reserve a minor amount (say 10 percent) of the reaction product produced by Equation 2 or 3 to catalyze a subsequent preparation of PSX and to treat the major portion of the reaction product according to the process of Equation 4 to obtain the desired end product.

When conducting the process of this invention, the relative amounts of sulfur and phosphorus trihalide are not critical. For economic considerations, it is usually desirable to employ an approximately stoichiometric quantity of reactants. However, it is not necessary to do so. Thus, it is possible to use a 20 mole percent or greater excess of either reactant. If an excess of reactant is desired, it is usually more economical to use the cheaper reactant, sulfur.

A catalytic quantity of complex is employed. Generally, an amount of catalyst within the range of from 0.05 to 0.5 mole of catalyst per mole of phosphorus trihalide is a suitable quantity. However, greater or lesser amounts can be employed if desired. Generally, from 0.075 to 0.3 mole of catalyst per mole of phosphorus trihalide yields satisfactory results.

In many instances, the reaction is exothermic and cooling means are sometimes required to maintain the reaction temperature at the desired level. The rate of mixing the reactants and catalyst can be used to control the temperature.

It is preferred to add the sulfur (or the phosphorus trihalide) to the other two ingredients.

The reaction time is not a truly independent variable and is dependent at least to some extent by the other process conditions used and the inherent reactivity of the reaction ingredients. In general, the reaction is complete in less than 10 hours; 5 hours or less being suflicient in many instances.

The following non-limiting examples illustrate the process of this invention. All parts are by weight. Example I demonstrates in some detail how the process of this invention can be embodied in a preparation of an alkyl phosphonothioic dihalide to accomplish re-use of aluminum values.

EXAMPLE I (l) Nitrogen flush a suitable reaction vessel and maintain a nitrogen atmosphere throughout the run. The vessel should be dry.

(2) Prepare a 10 percent PSCl preliminary mixture as follows:

(a) Charge 4.54 parts PCl and 0.43 part AlCl to the vessel.

(b) With stirring, heat to 60-65 C.

() Add 1.1 part sulfur incrementally at a rate to maintain the temperature between 60 and 70 C. After adding the initial increment, be sure the reaction has initiated (indicated by an exothermic reaction) before adding additional increments.

(3) Charge 9.6 parts sulfur to a kettle connected to the reaction vessel by a transfer line. Under N atmosphere, heat the second vessel to 140 C. to the melted sulfur.

(4) Add 3.9 parts AlCl to the reaction vessel.

(5) Heat the transfer line to 140 C. and the reaction vessel to 105 C.

h(61) Transfer the molten sulfur to the hot (105) (7) Form the rest of the PSCl to be used in this first stage by adding 40.86 parts P01 to the heelsulfur charge. Allow the reaction temperature to fall gradually to 65 C. as PSCl is formed. Attain 65 C. when about half the PCl is in and maintain the temperature at 65- 75 C. for remainder of feed. The reaction is exothermic.

(8) Add 28.9 parts of ethyl aluminum sesquichloride to the charge at a rate to maintain the temperature between 70 and 85 C. This is also an exothermic reaction.

(9) Remove 8.9 parts (10 percent) of the reaction mass which now contains ethyl phosphonothioic dichloride and the catalytic complex of that substance with aluminum chloride (see Equation 2 above). This will be used as a heel to catalyze the next sulfurization reaction. 'Store the heel under nitrogen atmosphere.

(10) Add 14.2 parts NaCl to the remainder of the cghlzglge. This amounts to one mole of NaCl per mole of (11) Reduce pressure to .50 mm. Hg and distill the product C H PSCl to a pot temperature of 130 C.

(12) Store the product in glass containers.

(13) Stop agitation and bring the system back to atmospheric pressure with nitrogen. The molten salt complex NaAlCL, will settle to the bottom.

(14) While hot (130 C.) the residue can be drained from the reaction vessel. The discharge lines should be heated to 130 C. to keep the salt from freezing.

(15) Repeat Steps 3 and 5-14 using the heel formed Step (9) to prepare another batch of C H PSCl EXAMPLE II Repetition of Example I with the exception that the ethyl aluminum sesquichloride is substituted with a molar equivalent of triethyl aluminum also yields the same product, ethylphosphonothioic dichloride. Similar results are obtained when the formation of PSCl from P01 and sulfur is catalyzed by the heel at 55, 70 and C. Likewise, similar results are obtained when the catalysis with AlCl is conducted at 55, 75 and 80 C.

EXAMPLE III A 500 ml. flask was flushed with nitrogen and charged with 68.8 grams of PCl and 6.5 g. AlCl The contents were stirred and heated to 50 C. After reaching this temperature, 16.2 grams of sulfur was added incrementally over a 15 minute period while maintaining the temperature at 5066 C. After all sulfur had been added, 34.2 grams of methyl aluminum sesquichloride was added dropwise over a 19 minute period. The reaction temperature rose rapidly to C. after addition of the sesquihalide was initiated. The temperature was allowed to fall to 40 C. (after all sesquihalide had been added). A 5 ml. sample of product which contained both CH PSCl and CH PSCl-AlCl was removed for catalysis of the second preparation discussed in the paragraph immediately below. The remaining reaction mass was worked up by adding 23.4 g. of NaCl and distilling the product at 163 and 43 mm. The yield was 83.9 percent of a product analyzing 97 percent CH PSCl and 2.2 percent PSCl The 5 ml. heel pulled was about equivalent to a 5 percent yield of CH PSCl Another run was made in the same manner as above except that the 5 ml. heel was substituted for the 6.5 g. of AlCl A product, 79.9 grams, analyzing 97 percent CH PSCl and 2.2 percent PSCl was obtained. Allowing 5 percent yield due to the heel the conversion of PSCl; to CH PSCl calculates to be 99 percent.

Similar results are obtained when the reaction of PC13 and sulfur catalyzed by the heel is conducted at 60 and 80 C.

When conducting these processes wherein the reaction heel is reserved for catalysis of a subsequent preparation of thiophosphoryl trihalide, the amount of heel reserved is usually governed by the amount of phosphorus halide and sulfur to be reacted in the next run. It is usually desirable to reserve an amount of catalyst which is sufficient to catalyze the subsequent reaction. Of course, if desired, a lesser amount of heel can be reserved and additional AlCl added to the next run.

EXAMPLE IV In a suitable reaction vessel, 16 g. of sulfur and a 5 ml. heel (prepared in a manner similar to the preparation given in Example III) was heated to 112 C. Phosphorus trichloride, 68.6 g., was added to the molten charge over a period of 10 minutes. Methyl aluminum sesquichloride was added over a period of 19 minutes (temperature 113132 C.). The resultant reaction mass was cooled to 30 C. and 25 g. of NaCl then added. Distillation at 50 mm., maximum liquid temperature C., yields 67.3 g. product which was over 99 percent pure CH PSClwith about 0.2 weight percent PSCl percent. The corrected yield was 84.6 percent.

Similar results are obtained if the heeled is used to catalyze the reaction of PSC1 and S at 120 C. or at 50 C.

Similar results are obtained if a chemically equivalent amount of trimethyl aluminum is substituted for the methyl aluminum sesquichloride.

EXAMPLE V A mixture containing 56.2 weight percent CH PSCl and 43.8 weight percent decane was prepared. A 'stoichiometric amount of AlCl (21.2 parts) was added to the CH PSCl 'AlCl was formed. This complex is separated from the decane layer and used to catalyze the formation of PSCl from phosphorus trichloride and sulfur as follows:

(a) A stoichiometric quantity of PC1 and S is reacted at 50 C. in the presence of 0.075 mole of catalytic complex per mole of PCI (b) A stoichiometric quantity of PCl and S is reacted at 120 C. in the presence of 0.3 mole of complex per mole of PCl (c) PCl and S, mole ratio 1.20:1, is reacted at 70 C. in the presence of 0.1 mole of CH PSCl -AlCl per mole of P01 (d) PCl and S, mole ratio 1.011.20 is reacted at 75 C. in the presence of 0.2 mole of catalytic complex per mole of PCl Various runs are summarized in this example. A catalytic complex is prepared by adding stoichiometric quantities of Reactant A and Reactant B. (These reactants are listed below.)

To the vessels containing the resultant complexes is added sulfur and then PCl such that the amounts of sulfur, P01 and catalyst are the same as in Example V(a). Reaction takes place at 50 C. In each instance the complexes catalyze the formation of PSCl Likewise, when the temperatures and relative amounts specified in V(b), V(c), and V(d) are used, the complexes listed above also function as catalysts for the'formation of PSCI Moreover, when the procedure of Examples I and II are followed except that the homologous aluminum sesquihalides and trialkyl aluminums having the alkyl groups set forth in Reactant A are employed, the compounds listed as Reactant A above are produced.

As an example of this, n-C H PSCl is prepared according to Example I by (i) formation of PSCl from PCl S and AlCl (ii) reaction of the PSCl thereby produced with to form the mixture of II'C3H7PSCI2 with its complex with AlCl (iii) reservation of a heel (that is a portion of this mixture) for catalysis of a subsequent reaction of PCl and S to form PSCl (iv) treatment of the remainder of the mixture with NaCl, KCl or dioxane to disrupt the complex.

(v) recovery of the C3H7PSC12 by distillation, and

(vi) repetition of Steps (i) to (v) except that the heel is used as the catalyst in Step (i) instead of AlCl The other compounds listed as -Reactant (A) above are prepared in like manner.

6 EXAMPLE v11 Substantially stoichiometric quantities of PBr and S are reacted at 60 C. using CH PSBr -AlBr as a catalyst to form PSBr On a mole basis, the amount of catalyst is 0.1 the amount of PBr Similar results are obtained when reaction temperatures of C., C. and C. are used. Similar results are obtained when the amount of catalyst is 0.075, 0.2, 0.3, 0.4, and 0.5 moles per mole of PBr EXAMPLE VIII Substantially stoichiometric quantities of PBr and S are reacted at 120 C. to form PSBr by conducting the reaction in the presence of 0.1 mole of C H PBr -AlBr per mole of PBR The same catalytic effect is obtained when a similar amount of the following catalysts are substituted, one at a time, for the catalyst used above.

Having fully described the process of this invention and its utility, it is desired that the invention should be limited solely by the lawful scope of the appended claims.

I claim:

1. A process for the preparation of a thiophosphoryl halide, said process comprising reacting sulfur and a phosphorus trihalide at a temperature of from about 50 to about 120 C., said process being catalyzed by a cata' lytic quantity of a catalytic complex having the formula RPSX -AlX wherein R is an alkyl group having up to six carbon atoms, and X is a halogen of atomic number 17 to 35.

2. The process of claim 1 wherein said complex is A1Cl3.

3. The process of claim 2 wherein said temperature is within the range of from about 60 to about 80 C.

4. The process of claim 3 wherein said catalytic complex is within the reaction product produced by reacting PSCl; and an alkylating agent selected from trimethyl aluminum and methyl aluminum sesquichloride.

5. The process of claim 1 wherein said complex IS C2H5PSCI2'AICI3- 6. The process of claim 5 wherein said temperature is from about 60-80 C.

7. The process of claim 6 wherein said catalytic complex is within the reaction product produced by reacting PSCl with an alkylating agent selected from triethyl aluminum and ethyl aluminum sesquichloride.

8. Process of claim 1 wherein said phosphorus trihalide is phosphorus trichloride.

9. Process of claim 1 wherein said phosphorus trihalide is phosphorus tribromide.

10. Process of claim 1 wherein R is propyl.

11. Process of claim 1 wherein R is butyl.

12. Process of claim 1 wherein 'R is hexyl.

13. Process of claim 1 wherein said phosphorus trihalide is phosphorus trichloride and said catalytic complex is C H PSCl -AlCl 14. Process of claim 1 wherein said phosphorus trihalide is phosphorus trichloride and said catalytic complex Is CH3PSCI2'A1C13- 15. Process of claim 1 wherein R is pentyl.

16. The process of claim 1 wherein said catalytic complex is within the reaction product produced by reacting PSX and an alkylating agent selected from the class consisting of R Al X and AlR wherein R is an alkyl group having up to six carbon atoms and X is a halogen of atomic number 17 to 35.

(References on following page) References Cited Kararanov et a1. Chemical Abstracts vol. 63 (1965) UNITED STATES PATENTS 3,458,569 7/1969 Melton 260-543 CHARLES B. PARKER, Primary Examiner OTHER REFERENCES 5 E. I. GLEIMAN, Assistant Examiner Okhlobystin et a1. Acadency of Science, USSR (1958') US. Cl. X.-R. pp. 977-979 (Eng. trans.). 

